This invention relates to a loudspeaker device and, more particularly, to a loudspeaker device capable of establishing phase-frequency characteristics independently from sound pressure (response)-frequency characteristics thereby to realize linear phase-frequency characteristics and flat sound pressure-frequency characteristics (i.e., completely realizing a transfer function which is 1).
Taking a three way speaker system for typical example, the system is composed of a woofer unit, a squawker unit, a tweeter unit, a network for dividing a signal into high, middle and low frequency bands and an enclosure for housing these component parts.
The multi-way speaker system is designed to achieve expansion of frequency range which can be sounded and a lower distortion factor. If, however, the sound pressure-frequency characteristics are flattened, the phase-frequency characteristics do not become linear as shown in FIG. 2 (a delay in the phase occurs generally in the low frequency range as compared with the high frequency range) thereby causing unnaturalness in hearing. The unnaturalness in hearing is caused by nonlinearity of the phase-frequency characteristics because a musical tone signal is composed of a fundamental wave and various harmonic components and, if each frequency range in which these harmonics are distributed is of a greatly different phase from that of the original tone, a waveform of a tone sounded from the loudspeaker becomes greatly different from that of the original tone, even though the sound pressure-frequency characteristics are flat.
The phase difference between frequency ranges described above is caused by an analog crossover network composed of a capacitor (C), a coil (L) and a resistor (R). More specifically, if the crossover network in the prior art device is constructed in such a manner that the sound pressure-frequency characteristics become flat, the phase-frequency characteristics also are changed with a result that the two characteristics cannot be made optimum simultaneously. In a case where other means for adjusting the sound pressure-frequency characteristics, e.g., a graphic equalizer, is employed, the problem that the phase-frequency characteristics are changed likewise takes place.
For realizing linearity in the phase-frequency characteristics of a loudspeaker, there are devices such as a device in which, as shown in FIG. 3, loudspeaker units (tweeter 10, squawker 12 and woofer 14) are arranged stepwise and a device employing an analog filter, i.e., an analog delay circuit for correcting phase in addition to a network for dividing a signal into several frequency bands.
In the device in which the loudspeaker units 10, 12 and 14 are arranged stepwise as shown in FIG. 3, however, projections and recesses are formed in an enclosure 16 with a result that the tone wave is seriously affected by diffraction thereby making realization of flattened phase-frequency characteristics difficult. Besides, since the correction of phase by this device is not an electrical phase correction, adjustment of the phase-frequency characteristics itself is also difficult.
In the prior art device employing the analog filter, there is the disadvantage that tone quality is deteriorated due to distortion caused in analog elements themselves.
It is, therefore, an object of the invention to provide a loudspeaker device capable of correcting phase independently from the sound pressure-frequency characteristics and thereby capable of realizing flat sound pressure-frequency characteristics and linear phase-frequency characteristics simultaneously without requiring a special arrangement of loudspeaker units which causes diffraction in a sound wave or a correction filter which causes deterioration in the tone quality.